In addition to the normal names used thus far, there are three
further classes:

1)

$: is used for self-reference, allowing
a verb to be defined recursively without necessarily
assigning a name to it, as illustrated
in Section 22.

2)

The names x and y are used in
explicit definition, discussed in Section 18.
They denote the arguments used in explicit definition.

3)

A name (such as ab_cd_)that has two
underbars of which one is the final character, is a locative.
Names used in a locale F can be referred to
in another locale G by using the suffix F
in a locative name of the form pqr_F_ ,
thus avoiding conflict with otherwise identical names in
the locale G .
See Section I of Part II
for further details.

The form of the display invoked by entering a name
alone is established by 9!:3 ,
as described in Appendix A.
For example: